Estimating the relative benefits of differing strategies for management of wastewater in Lower Egypt using quantifiable microbial risk analysis (QMRA)

The repport presents a practical example of how to operationalize the 2006 WHO Guidelines on the Safe Use of Wastewater, Excreta and Greywater and the recent World Bank Policy Research Paper 5412 on Improving Wastewater Use in Agriculture; An Emerging Priority. It describes a study carried out by the Univesrity of Leeds with the World Bank and the Holidng Company for Water and Wastewater of the Government of Egypt. The study used modern modeling techniques and a statistical tool known as Quantifiable Microbial Risk Assessment, by which the relative effectiveness of different wastewater management strategies can be assessed in terms of optimising health benefits to downstream populations. The study used a theoretical model of a typical drainage basin to assess what are the likely impacts on health of continuing GOEs policy of investing in additional aerated mechanical wastewater processes (primarily oxidation ditches and sequencing batch reactors) compared to the the use of natural wastewater treatment techniques, or marginal improvements in domestic septic tanks. The conclusions of the study sugegst that a more nuacned approach is needed with greater emphasis placed on increasing connection rates to existing treatment and improvements in at-house treatment. The study also provided an indication of how such methods could increasingly be used to enable the selection of cost-effective and appropriate wastewater management strategies.